Hi Trystan, great timing, I just have mine in use and could also invite you to have a look to my newly made topic New GSHP installation Vaillant VWF 58/4 with integrated DHW cylinder, 140m deep vertical loop
I’m seeing quite some difference between calculated heat/cooling and the heat reported by the unit.
If you like, you can also take a look to the data, started logging since yesterday: http://els23.dyndns.tv:8888/Energie/app/view?name=VaillantVWF584230V
This one is using the calculated heat based on flow rate and delta T.
I also have quite some feeds opened publicly, like the reported COP by the Vaillant unit.
A second one where I use the heat output reported by the Vaillant unit over eBUS:
http://els23.dyndns.tv:8888/Energie/app/view?name=VaillantVWF584_ebusd_data